Radioiodine whole-body scanning is one of the most sensitive techniques to detect recurrent thyroid cancer. Unfortunately, in order to raise serum tsh to stimulate radioiodine uptake in cells, patients must be withdrawn from thyroid hormone therapy for 4-6 weeks causing significant symptoms and signs of hypothyroidism. The present study, a 14 center study, was designed to test administration of recombinant human tsh to patients requiring radioiodine scans, but remaining on thyroid hormone therapy.